WARREN. — ALKALI-GRANITES AND PORPHYRIES. 241 



In several localities in the Hills, notably on the north and northeast 

 slopes of the Great Blue Hill and on the southern extension of Heniin- 

 way Hill, there are large outcropings of a porphyry in which the 

 feldspar phenocrysts are megascopically quite inconspicuous. The 

 cj^uartz phenocrysts are fairly numerous but small. The groundmass 

 is aphanitic and usually of a dark brownish red or purplish color. In 

 some places it appears to grade into the more crystalline porphyry 

 about it; in others the transition is sudden, almost sharp, although 

 always perfectly sealed. The sharpness of the transition here as with 

 the other types — granite, fine-granite and granite-porphyry ^ — is a 

 characteristic relation. 



In the region about Wampatuck Hill, the porphyry at the contact 

 with the aporhyolite is of the very dense quartz-porphyry variety. 

 The quartz phenocrysts are small and numerous, the feldspar is 

 megascopically suljordinate while the groundmass (where not strongly 

 weathered) possesses a peculiar yellowish-green color which the 

 microscope shows is due to the presence of many minute aegirite 

 microliths. Going away from the contact the rock changes within 

 a short distance — A-arying perhaps from 6 to IS inches — into the 

 variety with more abundant phenocrysts and this in turn changes 

 rapidly but gradually into the granite-porphyry of the Rattlesnake 

 Hill type. In the finer grained rock of the contact are many frag- 

 ments, clearly of the contact phase of the porphyry itself and others 

 seemingly of the aporhyolite. 



Along the easternmost portions of the contact with the felsite in 

 the Pine Hill Area, the porphyry at the contact presents a somewhat 

 different charcter. At the immediate contact it is of the dense quartz- 

 porphyry type and this shows breccia and flow-structures. \Yithin a 

 few inches this is succeeded quite suddenly by a coarsely porphyritic 

 type which is confined to this mode of occurrence. Here the feldspars 

 are larger and, when not broken or rounded, show acute terminations 

 approaching the "rhomben" type. They are often visibly broken 

 and resealed. In size they frec^uently measure a centimeter in length 

 by 5 to 7 mm. in Ijreadth by 3 to 4 mm. in thickness. The average is 

 somewhat under these figures. The quartz grains are fewer in num- 

 ber and also larger than in the run of the porphyry, sometimes 

 rivalling the feldspars in size. The groundmass is dense and usually 

 of a grey or bluish-grey color though in streaks and patches it is 

 greyish or yellowish-green. In this coarse porphyry near the contact 

 are streaks and fragments of the finer material. These are in part 

 portions of the coarse porphyry reduced to a fine-grained rock by 



